The processing of material such as semiconductor substrates involves the use of a variety of tools for performing various transfer and processing steps. Certain of the transfer and processing steps are performed in a vacuum chamber, while others are performed outside the vacuum chamber. As will be appreciated, throughput of the transfer and processing tools is an important factor in achieving low cost manufacture. Overall throughput is a function of both the processing time and the efficiency of automated substrate handling.
Automated substrate handling involves the movement of substrates from a substrate carrier to a processing station, and return of the substrates to the substrate carrier following processing. Various intermediate stations and transfer steps may be involved in this process. For example, substrate handling systems can include one or more load locks for transferring substrates to and from the vacuum chamber with minimal impact on the pressure level in the vacuum chamber. The substrate carrier may be a cassette, or a FOUP (Front Opening Unified Pod), which is a standardized carrier utilized for transporting substrates in fabrication facilities. Some of the processing and substrate handling operations may be performed concurrently to achieve efficient operation and high throughput. Accordingly, careful design of substrate handling systems is required.
Robots can be used outside of the vacuum chamber to transfer substrates from the FOUP or cassette to a load lock. Robots can be used inside the vacuum chamber to transfer the substrates from the load lock to a transfer station and/or a processing station. After the substrates have been processed, the robots reverse their actions so as to return processed substrates to the load lock. The load lock may then be vented and the substrates removed for storage.
All of the known substrate handling systems have one or more drawbacks, including but not limited to relatively low throughput, high cost and complex design. Accordingly, there is a need for improved methods and apparatus for transferring of substrates to and from a vacuum chamber.